1. Field of the Invention
The invention generally related to Fibre Channel load balancing and more particularly to the dynamic allocation of Fibre Channel traffic across multiple Fibre Channel paths.
2. Discussion of the Related Art
Fibre Channel is a gigabit-speed network technology used in storage networking. Fibre Channel is standardized in the T11 Technical Committee of the International Committee for Information Technology Standards (INCITS). Fibre Channel has become a standard connection type for storage area networks (SAN) in enterprise storage. Despite common connotations of its name, Fibre Channel signaling can run on both twisted pair copper wire and fiber-optic cables. For example, the Fibre Channel Protocol is a transport protocol similar to TCP used in IP networks which predominantly transports SCSI commands over Fibre Channel networks using various types of communication lines.
Advantages of Fibre Channel include high performance and exceptionally high data speeds, generally operating at 1, 2, 4, 8, 10, and 20 gigabits per second with relatively low noise, although other data speeds are anticipated. Additionally, fiber optic technology overcomes traditional input/output (I/O) channel distance limitations at gigabit speeds. Fibre Channel is also more lightweight than bulky copper cables and is operable to transport a wide variety of protocols.
Fibre Channel supports three different topologies, point-to-point, fabric attached, and arbitrated loop. The point-to-point topology is the simplest topology that attaches two devices directly. The fabric attached topology attaches a device directly to a “fabric”. In this regard, devices or loops of devices are connected to Fibre Channel switches, conceptually similar to modern Ethernet implementations. The arbitrated loop topology attaches devices in a loop, or “ring”, similar to token ring networking. Adding or removing a device from the loop causes activity on the loop to be interrupted. Furthermore, a failure of one device causes a break in the ring. Thus, Fibre Channel hubs exist with “failover” links such that failed ports may be bypassed.
In the arbitrated loop topology, up to 126 devices and one connection to a fabric switch may exist in a single arbitrated loop physical address space. Data within an address space physically travels from node to node in a daisy-chain fashion, ultimately traveling in a loop. Control by a device on the loop is obtained through the process of loop arbitration, after which the device winning arbitration sends data. In a half duplex mode, only one device transfers data at any point in time. In a full duplex mode, two devices may communicate with each other at the same time over a single interconnective segment of the loop. In the absence of load balancing, Fibre Channel traffic is generally handled on a “first-come first-served” queuing.
Fibre Channel communications, however, are often configured in a plurality of Fibre Channel loops. For example, a single Fibre Channel arbitrated loop may be configured with multiple devices that communicate through the loop with a host computer. This topology can be extended by way of a host bus adapter that connects multiple loops to the host computer such that the host computer may communicate with each Fibre Channel loop and the devices thereof. While this topology provides the host computer with more resources, these resources typically have competing interests that require some form of load balancing.
In computing, load balancing is a technique that spreads work around processing nodes (e.g., computers, network links, CPUs, hard drives, etc.) in order to maximize throughput and minimize response time. An example of one such technique employed in Fibre Channel communications includes a “Round Robin” technique that attempts to balance I/O requests across multiple paths by sequentially selecting the paths for each I/O request. In this regard, a multiplexer, switch, or router may employ a round-robin scheduling algorithm using a separate queue for every data flow with each being identified by its source and destination address. The scheduling algorithm allows every active data flow having data packets in queue to take turns transferring packets on a shared channel in a periodically repeated order.
Over time, each path in a Round Robin scheduling supposedly has an average utilization. However, this type of scheduling does not take into consideration other factors that affect load balancing. For example, Round Robin scheduling algorithms do not account for variations in the operation or configurations of multiple paths.